How to use this calculator
- Enter or choose heat transfer coefficient (h).
- Enter or choose surface area.
- Enter or choose surface temperature.
- Enter or choose fluid temperature (away from the surface).
- The heat flow from the surface updates as you type. Use Copy result or Share to keep it.
Method
Q̇ = h × A × (T_s − T_∞); R_conv = 1 ÷ (h × A)
- h
- convective heat transfer coefficient
- A
- surface area in contact with the fluid
- T_s
- surface temperature
- T_∞
- bulk fluid temperature
Worked example
- ΔT = 80 − 20 = 60 K.
- Q̇ = 25 × 2 × 60 = 3000 W (1500 W/m²).
- R_conv = 1 ÷ (25 × 2) = 0.02 K/W.
A 2 m² surface at 80 °C in moving air at 20 °C with h = 25 W/(m²·K) loses about 3 kW by convection.
What the result means
A positive result is heat leaving the surface. Hot surfaces also lose heat by radiation, which can be similar in size for still air, so add the Stefan–Boltzmann result for a total.
Assumptions and limits
- h is uniform over the surface and known.
- Temperatures are steady.
- h is an estimate unless taken from a correlation (Nusselt number) for your geometry and flow; results are only as good as h.
Questions
How do I get a better value of h?
Use a Nusselt-number correlation for your geometry (flat plate, pipe, cylinder) with the Reynolds or Rayleigh number, or measured data.
Is this the same as Newton’s law of cooling?
Yes. Newton’s law of cooling states that the convective heat loss is proportional to the temperature difference, with h as the constant.